The invention relates to a mold for shaping elongated, softened plastic products and more particularly to shaping such products into an arcuate configuration.
Plastic hollow sections for window frames have found wide spread use where the usually plane window borders and frames make it easy to use basically plane special plastic sections for such purposes. The advantages of such sectional construction, highly developed since their inception, have resulted in a need for curved sections of special shapes, particularly when repairing older buildings. Basically, it has been possible to prepare such arches for a long time, particularly according to to a more recent process where preshaped sections are dipped into a special liquid and are heated to a predetermined temperature, 120.degree. C., for instance. Thereafter the sections are easily shaped.
The customary shaping process, however, is afflicted with difficulties. When the sections are bent over a template or are bent within a mold, bulge waves and bulge folds occur along the internally located areas of the arches which depend on the properties of the sections. Furthermore, such specialized arches result in large costs and are time consuming to manufacture due to the relatively large amount of labor because changed arch shapes regularly require new molds or at least molds which are varied sectionally by joining parts thereof. Such dismountable molds frequently result in unacceptable products. These problems which occur frequently in the production of windows are basically applicable not only for these products but generally when forming complicated plastic sections.
An object of the present invention is to provide for the shaping of straight plastic sections into arcuate shapes simpler and more securely as well as more flexibly in respect to various arcuate shapes in order to obtain better and cheaper parts.
According to the invention this objective is achieved with a mold or template according to the disclosure which follows.
In applicant's invention, a mold formed by flexible guide rails allows the curvature of the template to be varied in an easily understood manner by more or less intensive bending in an elastic or a plastic mode and to produce thereby a fast accommodation to varied radii or shapes. Experimental sample or trial arches or arcuate shapes may be prepared and it is also possible to change a shape that is distorted due to cold-flow by correcting such effects. Such corrections may be achieved costing little labor or time. A mold constructed according to such a principle allows also an uninterrupted support for the formed shape which is at least at the beginning relatively soft and does so in the particularly critical inner and outer areas. It creates thereby good conditions for a product free of damages and irregularities or almost free of such defects.
The construction of the mold by aid of guide rails has shown particularly that the work piece may be pulled longitudinally through the mold thereby not only resulting in a steady and well controlled shaping process but also is particularly apt to prevent bulge waves and bulge folds.This procedure of shaping has shown that the customary frequently occurring danger of bulge waves and bulge folds is prevented and that now, after each hardening process, a plastic section may be removed from the mold which is uniform as to its cross section and has a smooth surface. An advantageous embodiment allows entry laterally into the mold with a drawing tool and to pull in this mold a section, held by its head, while the drawing tool follows the mold longitudinally.
A particularly advantageous mold allows the use of an extremely strong and rigid or tough material for the parts of the mold like polyethylene, particularly ultrahigh molecular low pressure polyethylene without restrictions when light variations of curvatures occur. Continuous rear edges allow the use of the bending strength of such a material and to retain its property of a sliding or slippery material and still retain the required bendability. While the mold parts change their shape exclusively in their rear area, their cross sectional shape is not impaired. The recesses intruding from the edge particularly prevent dislocations of the material caused by the curvature which could impair the cross sectional shape of the mold.
Other features which are considered characteristic of the invention are set forth in the appended claims.
Although the invention is illustrated and described in relationship to specific embodiments, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.